To facilitate an understanding of the invention as a novel solution to the problems presented by multiple incompatible protocol stacks, a number of basic local area network (LAN) concepts are described herein. Essentially, a LAN comprises a system of devices, such as computers, printers and other computer peripherals, which are communicatively coupled together to provide resource sharing and/or data sharing. Resources and data are shared by allowing these network devices, referred to as nodes, to communicate with other nodes on the network and to request or offer data and services from or to other nodes. By way of example, file servers are common network nodes which allow other nodes to access files stored on the file servers.
At a fundamental level, LANs provide a frame-work for clients, servers, and other devices to communicate. The frame-work includes physical components such as interface cards, memory buffers, voltage regulators, cabling and the like, which physically connect the nodes. In addition, the framework includes device drivers and other software operating instructions which are executed by the nodes and which control the operation of the physical components. For example, operating instructions enable a client to communicate with other nodes using specific known protocols referred to as protocol stacks or suites. A client's protocol stack modifies its outgoing and incoming data to a form which its physical components can transmit or receive over the network.
When modifying outgoing data generated by an application running on the client, the protocol stack transforms the outgoing data into a series of discrete packets which are then transmitted, usually serially, over physical cabling. Specifically, the protocol stack accepts a number of bits of data to be sent and then prepends or appends additional bits for purposes including error correction, broadcast source node identification, and receiving or destination node identification. The specific modifications depend upon the specific type of protocol being implemented. After creating a modified packet of data, the protocol stack passes the packet to a hardware processing stack of the client which adds hardware specific bits according to the physical configuration of the client.
Conversely, upon receipt of an incoming packet of data, the hardware stack of the client strips the packet of its hardware specific bits, and sends the packet to the protocol stack. Then, the protocol stack strips off the error correction and other protocol specific bits from the packet and sends the data to a destination application.
In 1978, the International Organization of Standards, a world-wide standards setting body, created a network reference model known as the Open Systems Interconnection (OSI) model. The OSI model currently includes seven different conceptual layers: 1) The Physical layer which defines the physical components connecting the node to the network; 2) the data link layer which controls the movement of data in discrete forms known as frames and which arranges the data to identify various fields; 3) The Network layer which builds data packets and indicates the type of frame which has been built or must be built by the Data Link layer following a specific protocol; 4) The Transport layer which ensures reliable delivery of data by following a specific protocol which adds to the error correction facilities of the lower levels; 5) The Session layer which allows for two way communications between nodes by controlling communication transfers between connected nodes; 6) the Presentation layer which controls the manner of representing the data, e.g. ASCII or EBCDIC, and ensures that the data is in correct form; and 7) The Application layer which provides protocols and routines for file sharing, message handling, printing protocols and the like. The OSI model has been generally accepted as a reference model for comparison purposes even though many LANs cannot readily be delineated into each of the above-defined layers.
Many early LANs were designed to operate with the specific hardware of the clients running on the LAN, including the network interface cards (NICs) of the clients which provide part of the clients' physical connection to the network itself. These types of LAN designs are largely implemented through programs running on the client, known as network drivers, which control communication with the network utilizing the particular physical configurations.
A major limitation associated with the hardware specific nature of these LANs was that a client could only operate one network layer protocol stack at a time. The client was limited in this manner because each network driver of the client attempted to control the same physical hardware. Due to the asynchronous nature of LAN communications, these drivers had difficulties synchronizing with other drivers which attempted to control the same physical components at the same time. As a result, the client was limited to the operation of a single network layer protocol stack and was not able to simultaneously attach to multiple nodes on a network which were implementing different protocols.
To allow a client to implement more than one network layer protocol, multiple protocol drivers were designed and developed consisting of a single network driver which controls the physical components of the client while allowing the client to implement many commonly used protocol stacks at the same time. Multiple protocol network drivers include two components. First, they provide a single generic interface for hardware designers and protocol designers who need only design their products for a single well-known and well-defined generic interface regardless of the physical components. The generic interface allows the client machine to operate more efficiently by eliminating the need for the client to load and operate a specific driver for every specific protocol.
A second component of multiple protocol drivers is a stack manager which directs data packets to or from the generic interface to or from its appropriate protocol stack. The stack manager operates by acknowledging and binding a protocol stack to the generic interface. Multiple protocol drivers through the stack manager maintain a record of the number and kind of protocol stacks which are loaded into the client's memory.
The client and the multiple protocol network driver operate in the following manner. A client loads, as part of its initialization process, the multiple protocol network driver into memory. Thereafter, multiple compatible protocol stacks may be loaded into memory and bound to the driver. A protocol stack is compatible if the network driver can properly transmit and receive packets from or to that protocol stack without affecting the proper operation of other protocol stacks which are also bound to the driver.
The loading of the various compatible protocol stacks is supervised by the network driver's stack manager which constructs and stores the records necessary to bind each protocol stack to the single driver. Following the steps of loading and binding each protocol stack, client applications may begin to communicate with the network using the bound protocols. To send data to the network, an application will pass the data to be transmitted to a particular protocol stack. The protocol stack implements the protocol and then passes the resulting packet to the generic interface of the driver. In turn, the generic interface accepts the packet and further places it into a well-defined form for transmission by the physical components. Subsequently, the physical components, utilizing the well defined form of the packet, modify the packet according to hardware specifications and transmit the packet to the network.
For incoming data from the network, the sequence of receiving a packet from the network is essentially the reverse process of transmitting a packet. An NIC of the physical components receives an appropriate incoming packet from the network and determines that the packet is destined for the client. The NIC passes the packet to the hardware stack which strips off hardware specific bits and passes the packet to the generic interface. The stack manager of the driver analyzes the packet and then passes the packet to the appropriate protocol stack. Finally, the protocol stack rebuilds the data from the packet stream and passes the data to the application.
As noted above, the multiple protocol drivers can only properly operate with compatible protocol stacks. Usually, a protocol stack is compatible when the stack has been designed to produce and receive packets in the well-defined form utilized by the driver's generic interface. However, even those protocol stacks which are operable with the generic interface may still be incompatible with other protocol stacks. For example, a subsequent protocol stack which implements a protocol that a prior protocol stack is already implementing is incompatible because the driver's stack manager is not able to ascertain to which of the two stacks using the same protocol incoming data should be routed.
The inability of the network driver to operate two protocol stacks which implement the same protocol is generally not problematic for unsophisticated operation of client machines because applications wishing to use a certain protocol may only need to interface with one protocol stack. However, for more sophisticated operation of a client machine, a need arises for the client to run two protocol stacks which do implement the same protocol. One example of a need to simultaneously run two protocol stacks of the same type occurs when an application is using a protocol stack in the Microsoft.RTM.MS-DOS.RTM. operating system environment (real mode) and another application attempts to use a Microsoft.RTM. Windows.TM. operating system (protected mode) version of the same protocol stack.
To establish an MS-DOS.RTM. real mode multiple protocol environment, the client loads the multiple protocol network driver, the real mode protocol stack, and any other compatible protocol stacks into specific areas of its random access memory, called conventional memory. These programs and protocol stacks operate as terminate and stay resident programs (TSRs) which are always in RAM and are usually activated by interrupts generated either by physical hardware, which signifies an incoming data packet from a remote node, or by software interrupts made by MS-DOS.RTM. routines attempting to send data to a remote node. These TSRs are said to operate in real mode because they reside in a highly specified and crowded area of RAM called conventional memory. The operation of these TSRs in this area of memory often causes conflict with other programs and data which also require access to this area of RAM. Moreover, most TSRs will under-utilize the capabilities of the client because the TSRs are not designed to work in conjunction with multi-tasking operating systems.
In a Windows.TM. protected mode operating system environment, the network drivers, protocol stacks, and other layers are loaded into areas of RAM above conventional memory, either expanded or extended memory, depending on how the Windows.TM. operating system perceives the memory needs of the client. The capacity of extended or expanded memory may be vastly greater than conventional memory and, as a result, far fewer memory conflicts with other applications occur in these areas. Additionally, the Windows.TM. operating system acts to intercept interrupts and further acts as an intermediary between the network layers and the microprocessor thereby allowing the client machine to perform multi-tasking.
As discussed above, once a real mode protocol stack has been loaded and is operating, it is not possible to run a subsequent protected mode version of a protocol stack which implements the same protocol because the stack manager is not able to differentiate between the two protocol stacks. A solution would be to terminate the real mode protocol stack and transfer communication responsibilities of the applications using the real mode protocol stack to the protected mode protocol stack. Unfortunately, it is tremendously difficult if not, as a practical matter, impossible, to entirely switch from a real mode to a protected mode of operation and still properly maintain and service the prior real mode network connections.
Therefore, in order for a client to maintain existing network connections and still take advantage of the protected mode of operation for subsequent connections, a need exists for the client to be able to concurrently provide a real mode and protected mode protocol stack of the same type.